Apparatus for sealing a cover foil to a blister foil

ABSTRACT

A cover foil is sealed to a foil formed with an array of blisters by a drive roller centered on an axis and having a generally cylindrical outer surface formed with an array of outwardly open recesses complementary to the array of blisters. The outer surface is annularly continuous and formed of an at least limitedly elastically deformable material. The roller further is formed inward of the outer surface with at least one pressurizable chamber. The blister foil engages the drive roller with the blisters fitting into the recesses. A sealing roller presses a cover foil radially against the blister foil on the drive roller and thereby seals the cover foil to the blister foil between the blisters. A source of compressed air is connected to the drive roller for pressurizing the chamber and thereby changing a circumference of the drive-roller outer surface and an angular spacing between the recesses.

FIELD OF THE INVENTION

The present invention relates to an apparatus for heat-sealing two foils together. More particularly this invention concerns such an apparatus that heat seals a normally planar cover foil atop a foil formed with an array of product-filled blisters.

BACKGROUND OF THE INVENTION

It is standard practice to package medicaments in multiple blister packs constituted by a base foil formed with an array of pockets or blisters each holding one or more objects, e.g. pills, and a flat cover foil that is heat sealed onto the blister foil to close the pockets, thereby hermetically containing the objects. Such packaging allows very delicate objects to be safely contained, yet still leaves them visible and easy to get at.

As a rule both the foils are dispensed from rolls. The blister foil has is moved horizontally with its blisters open upward under a filling machine that puts the objects in the blisters. As described in German patents 103 41 450 and 103 47 777 the blister foil passes tangentially past a lower drive roller whose outer surface is formed with an array of recesses matching the array of blisters, with the blisters fitting into the pockets. The cover foil is pressed by a heated smooth roller atop the drive roller to fuse the cover foil to the blister foil in the webs between the blisters.

Such an arrangement requires that the blisters be perfectly centered in the recesses of the lower drive roller. If they get offset and pinched, the blisters can be damaged along with their contents. Since the foil is heated and the rollers are heated, this can happen due to unavoidable thermal expansion or stretching caused by tension in the foils. The result is a damaged package that must be culled out, something that can be expensive when a valuable medicament is being packaged.

Accordingly, DE 10 2004 010 202 of Riekenbrauck uses a drive roller whose outer surface is formed by two semicylindrical shells that can be moved limitedly radially to vary the effective radius of the drive roller. Thus some limited compensation can be made when the blisters shift off-center. Under the best of conditions, however, the spacing of the recesses on each shell remains the same so that the compensation is crude and cannot often make up for a substantial change in, for example, blister-to-blister spacing.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved apparatus for sealing a cover foil to a blister foil.

Another object is the provision of such an improved apparatus for sealing a cover foil to a blister foil that overcomes the above-given disadvantages, in particular that can accurately compensate for small or large changes in blister spacing.

SUMMARY OF THE INVENTION

An apparatus for sealing a cover foil to a foil formed with an array of blisters has according to the invention a drive roller centered on an axis and having a generally cylindrical outer surface formed with an array of outwardly open recesses complementary to the array of blisters. The outer surface is annularly continuous and formed of an at least limitedly elastically deformable material. The roller further is formed inward of the outer surface with at least one pressurizable chamber. The blister foil engages the drive roller with the blisters fitting into the recesses, and the drive roller is rotated about the axis to advance the blister foil. A sealing roller presses a cover foil radially against the blister foil on the drive roller and thereby seals the cover foil to the blister foil between the blisters. A source of fluid under pressure is connected to the drive roller for pressurizing the chamber and thereby changing a circumference of the drive-roller outer surface and an angular spacing between the recesses.

More particularly according to the invention sensor means upstream of the drive roller detects a spacing between the blisters of the blister foil, and control means connected to the sensor means and to the pressurizing unit adjusts the pressurization of the chamber such that the spacing of the recesses is substantially equal to the detected spacing of the blisters.

The surface is of one-piece construction and is in fact formed by an annularly continuous tubular sheath whose circumference can be adjusted in the range of the elastic ductility of the material the drive roller is composed of, due to the pressure in the chamber, so that, with a fixed rotation axis of the drive roller, adjustment of the spacing between adjacent recesses in the outer surface is made exactly equal to that between the blisters of the blister foil. This adjustment occurs quickly, as the drive roller follows the exterior force effect with low mechanical inertia.

For this purpose it is therefore advantageous for the invention, if the drive roller is composed of a material having a low modulus of elasticity. This way, using low pressure, comparatively big changes regarding the circumference of the drive roller's outer surface can be achieved, which consequently only shows little resistance to an adequate force effect. It is especially advantageous if the drive roller is composed of a material that has a lower modulus of elasticity than a metal, which means that therefore plastic is an advantageous material for the outer surface of the drive roller.

Concerning the favorable mechanical, but also chemical characteristic, it is to be preferred if the drive roller is composed of polytetrafluoroethylene (PTFE) that has a modulus of elasticity of 420 Newton per square millimeter that is significantly lower than aluminum with 69,000 Newton per square millimeter.

Under operational conditions exceeding the load capacity of PTFE, polyamide can be used as an alternate plastic.

In the framework of the invention it is furthermore preferable if several chambers are provided, in order to be thus able to provoke a bigger adjustment of perimeter and to avoid a deformation of the geometric shape of the outer surface of the drive roller.

It has thereby proven to be of use if the drive roller has a hub with spokes protruding in the direction of the outer surface and separating the chambers evenly spread over the circumference and forming chamber walls. Furthermore the spokes serve to transmit torque from the hub to the outer surface.

In order to simplify the production as well as the maintenance of the drive roller, it is convenient if the chamber is closed by two cover disks axially flanking the drive roller. It thereby has to be considered that the covers themselves do not have to undergo a change of length in circumferential direction caused by pressure changes in the chamber, but only ensure that no pressure drop takes place in the chamber, even if subsequently to the changing pressure conditions the diameter and outer circumference of the drive roller change. In order to guarantee the necessary density during the operating process of the apparatus, it is furthermore provided that the two lateral covers are connected through one, or if necessary more, bolts extending through the chamber to ensure that the two covers safely seal the chamber without thereby influencing the symmetric deformation of the drive roller.

In principal it is possible to feed the pressure medium into the chamber by means of an elastic pressure medium supply 15 line, rotatably connected to the drive roller. As far as a high operational security is concerned it is, however, of advantage to renounce such an elastic pressure medium supply line and to connect, according to the invention, the pressure medium supply line to the pressure medium source through a rotary transmission coupling.

In order to avoid shear on mispositioning of the recesses in relation to the blisters in the blister foil and to be able instead to preemptively prevent such a situation, the appparatus is provided with a sensor as part of a control system for determining the position of a blister in the blister foil, so that the perimeter necessary for a correct positioning of the blister in the recesses can be set in the drive roller by adequate pressurization of the chamber.

It is furthermore favorable if a sensor for determining the temperature of the drive roller is provided, since particularly if plastic is chosen as material for the drive roller, the thermal conductivity is reduced compared to metal and the heat applied by the sealing roller is controlled and the changes in volume of the drive roller caused by the change of temperature can be considered when the outer circumference of the drive roller is determined.

In order to cause outer circumference changes of the drive roller which are as flexible as possible, the pressure medium supply line has a proportioning valve and/or a manifold valve that are used to precisely set a desired pressure or switch between several levels of pressure.

To avoid damage to the drive roller when it is made of a plastic, it is useful if a sensor is provided for detecting the presence of the cover foil and the blister foil between the drive roller and the sealing roller, since, dependant on the sensor signal, the sealing roller can be lifted from the drive roller pr the drive roller can be dropped if foils are missing.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a schematic, perspective view of a appparatus according to the invention;

FIG. 2 is a perspective view of the drive roller without the covers that close its chamber;

FIG. 3 is a side view of the drive roller from FIG. 2 with the force effect during pressurization of the chambers shown by arrows; and

FIG. 4 is a cross-sectional view of the drive roller with the structural components needed for its use.

SPECIFIC DESCRIPTION

FIG. 1 shows an apparatus for sealing a blister foil 1 containing filled blisters 2 and a cover foil 3, both the blister foil 1 and the cover foil 3 being pulled from unillustrated supply rolls and fed, if necessary over deflecting wheels, to a nip between a heated sealing roller 8 and a drive roller 5 centered on respective axes 8A and 5A. The drive roller 5 is drivable by means of a roller drive 4 and has recesses 6 for the blisters 2 of the blister foil 1 in its outer surface.

In addition as shown in FIGS. 2 and 3, the drive roller 5 has a plurality of chambers 15 connected to a source 17 of air under pressure by a conduit 16. The drive roller 5 is composed of a material which has a modulus of elasticity that is significantly lower than for example that of a metals with a modulus of elasticity for example of aluminum of 69,000 Newtons per square millimeter. Suitable materials are plastics and among these in particular are polytetrafluoroethylene (PTFE) with a modulus of elasticity of PTFE of 420 Newton per square millimeter, so that a drive roller 5 made of it can easily be elastically deformed to effect an outer circumference enlargement of about 0.5 mm and by pressurization with about 15 bar. These changes are sufficient to effect the necessary minor corrections of the spacing of the recesses 6 in relation to the blisters.2. The same pressure is supplied to all of the multitude of chambers 15, as illustrated in FIG. 2, because the drive roller 5 has a hub 7 with radially projecting spokes 10 separating the chambers 15 angularly from one another.

In addition the chambers 15 are closed by two cover disks 11 that axially flank the drive roller (FIG. 1). The two cover disks 11 are connected to each other through spacer bolts 14 that each extend centrally a respective one of the chambers 15. This way the chambers 15 are axially closed, an effect that can be enhanced by providing each axial face of each chamber 15 with an unillustrated O-ring. The conduit 16 is connected to the pressure medium source 17 by means of a rotary coupling 12, so that the rotationally drivable drive roller 5 can be supplied with compressed air, the necessary pressure medium, without difficulty.

The apparatus furthermore has a sensor 9 as part of a controller 18 for determining the position of a blister 2 of the blister foil 1 (FIG. 1), in order to determine the correct position of the recesses 6 in relation to the blisters 2 coming to the recesses 6 by determining the position of these blisters 2 and the known transfer speed of the blister foil 1 as well as the lo known rotation speed of the drive roller 5. For a further improvement of the operational reliability, the apparatus is additionally provided with a sensor 20 for determining the temperature of the drive roller 5, as well as with a sensor 19 for determining the presence of the cover foil 3 and the blister foil 1 between the drive roller 5 and the sealing roller 8, in order to avoid contact of the heated sealing roller 8 with the plastic surface of the drive roller 5. A proportioning valve 13 or and/or a manifold valve is provided in the conduit to control the pressure in the chambers 15. 

1. An apparatus for sealing a cover foil to a foil formed with an array of blisters, the apparatus comprising: a drive roller centered on an axis and having a generally cylindrical outer surface formed with an array of outwardly open recesses complementary to the array of blisters, the outer surface being annularly continuous and formed of an at least limitedly elastically deformable material, the roller further being formed inward of the outer surface with at least one pressurizable chamber, the blister foil engaging the drive roller with the blisters fitting into the recesses; means for rotating the drive roller about the axis and thereby advancing the blister foil; means including a sealing roller for pressing a cover foil radially against the blister foil on the drive roller and sealing the cover foil to the blister foil between the blisters; and means connected to the drive roller for pressurizing the chamber and thereby changing a circumference of the drive-roller outer surface and an angular spacing between the recesses.
 2. The sealing apparatus defined in claim 1, further comprising: sensor means upstream of the drive roller for detecting a spacing between the blisters of the blister foil; and control means connected to the sensor means and to the pressurizing means for adjusting the pressurization of the chamber such that the spacing of the recesses is substantially equal to the detected spacing of the blisters.
 3. The sealing apparatus defined in claim 1 wherein the surface is made of a material having a smaller modulus of elasticity than metal.
 4. The sealing apparatus defined in claim 3 wherein the material is plastic.
 5. The sealing apparatus defined in claim 4 wherein the material is polytetrafluoroethylene.
 6. The sealing apparatus defined in claim 4 wherein the material is a polyamide.
 7. The sealing apparatus defined in claim 3 wherein the surface is formed by a tubularly cylindrical sheath.
 8. The sealing apparatus defined in claim 7 wherein the drive roller is formed with a plurality of the chambers angularly spaced about the axis.
 9. The sealing apparatus defined in claim 8 wherein the drive roller has a hub radially inwardly delimiting the chambers and spokes angularly delimiting the chambers and connected to the sheath.
 10. The sealing apparatus defined in claim 9 wherein the hub, spokes, and sheath are unitary.
 11. The sealing apparatus defined in claim 9 wherein the drive roller has a pair of axially spaced face disks axially delimiting the chambers.
 12. The sealing apparatus defined in claim 11 wherein the disks are generally planar and have outer diameters smaller than an outer diameter of the sheath.
 13. The sealing apparatus defined in claim 11 wherein the drive means further comprises axially extending bolts having ends pressing the disks against the hub, spokes, and sheath.
 14. The sealing apparatus defined in claim 13 wherein one such bolt extends axially through each chamber.
 15. The sealing apparatus defined in claim 1 wherein the drive roller has a shaft and the means for pressurizing includes a coupling connected to the shaft.
 16. The sealing apparatus defined in claim 1, further comprising sensor means for detecting a temperature of the sealing roller.
 17. The sealing apparatus defined in claim 1 wherein the pressurizing means include valve means for varying the pressurization of the chamber.
 18. The sealing apparatus defined in claim 1, further comprising means for detecting the presence of the foils between the rollers.
 19. The sealing apparatus defined in claim 1 wherein the means for pressurizing pumps air into the chamber.
 20. The sealing apparatus defined in claim 1 wherein the chamber is so constructed that when it is pressurized only its outer diameter changes. 